This invention relates in general to sheet material conveyor loading apparatus and deals more particularly with improvements in apparatus of the type wherein sheet material to be loaded onto a belt conveyor is pulled by the conveyor from an adjacent supply table. In an apparatus of the aforedescribed general type some means is provided for clamping or otherwise releasably securing to the conveyor a portion of the sheet material to be loaded so that the sheet material travels onto and with the conveyor as it is pulled from the supply table. In some instances it is essential that the sheet material be loaded and advanced with precision. This is particularly true in a conveyorized programmable apparatus for working on sheet material wherein a tool moves in working relation to sheet material supported on the conveyor in response to command signals received from a programmable controller. In a machine of the aforedescribed general type, which may, for example, be used to cut pattern pieces from successive segments of long lengths of sheet material, it is essential that the material be loaded onto and advanced with the conveyor with precision, so that proper relationship between pattern pieces cut from successive segments of the material is maintained to avoid overlapping cuts and resulting waste. If the machine includes a vacuum holddown conveyor for holding sheet material in fixed position on the conveyor while it is worked upon, it is usual to utilize the vacuum holddown function of the conveyor to releasably secure at least a portion of the sheet material to the conveyor to move with the conveyor during the conveyor loading and advancing mode. However, application of vacuum holddown force to the conveyor belt during the material moving mode generally increases frictional engagement between portions of the conveyor belt and associated portions of its supporting structure, which results in a corresponding increase in the power required to move the conveyor. When vacuum is applied to the holddown conveyor during the material moving mode it also becomes more difficult to precisely control conveyor movement for proper material positioning. Further, a zoned vacuum holddown conveyor is usually required for such an apparatus, which substantially increases the cost of producing the apparatus.
Accordingly, it is the general aim of the present invention to provide an improved apparatus for loading sheet material onto a conveyor. A more particular aim of the invention is to provide an improved loading device suitable for use with a vacuum holddown conveyor to secure sheet material to the conveyor during the material moving mode whereby to eliminate the need for application of vacuum to the conveyor while the conveyor is in motion.